Work out how much water your pond actually holds.
Use the average water depth—not simply the deepest point. Shelves, sloping sides, rocks and planting baskets all reduce the real volume.
Starting circulation range
2,400–4,800 litres per hour delivered at the pond.
Illustrative 25% allowance6,000 litres per hour before checking head loss.
The correct pump must also suit the filter’s recommended flow, vertical lift, hose size, pipe length, bends, waterfall and any flow split. Pressure-filter maximum flow must never be ignored.
How to measure an irregular pond
Measure the longest length and widest width, then take several depth measurements. Add the depths together and divide by the number of measurements to obtain an average. For a strongly curved or kidney-shaped pond, reduce the rectangular result to allow for the missing corners. If accuracy matters—for treatments or fish loading—a water meter used while filling is better than geometry.
What the circulation figures mean
A complete circulation roughly every one to two hours is a useful early planning range for many ordinary garden fish ponds, but it is not a universal rule. A heavily stocked koi pond can need more filtration and aeration; a wildlife pond may need much less mechanical circulation. The filter manufacturer’s stated flow range and the pump’s performance curve remain decisive.
Why the pump-box figure is not delivered flow
The headline litres-per-hour rating is normally measured with little or no lift and minimal restriction. Real output falls when water is pushed uphill, through narrow or long hose, around bends, through valves and into a pressurised filter. Use the pump performance graph at the calculated head, not just the name printed on the box.